G5 Imac power supply swap-out question.

M

mikeyjd

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I have a 20" G5 IMac 1.8ghz and I believe that the power supply unit is playing up. Before I order a replacement I was considering swapping it with the supply from my 17" G5 1.6ghz to confirm the problem. Anyone know if this is likely to cause any damage/problems. Will the unit fit? they look similar.

Both IMac's are circa 5 years old (non ambient light models)

Thanks
 
You'll discover that the power supplies cannot be swapped between a 17 and 20-inch iMac. They are similar in size, but the mounts are different. You CAN plug one in to the other, and test while the back cover remains off, just to test for a completely dead power supply.
Usually, if you suspect one of those iMac power supplies - you are usually correct.
 
DeltaMac said:
You'll discover that the power supplies cannot be swapped between a 17 and 20-inch iMac. They are similar in size, but the mounts are different. You CAN plug one in to the other, and test while the back cover remains off, just to test for a completely dead power supply.
Usually, if you suspect one of those iMac power supplies - you are usually correct.
Click to expand...

Thanks for the prompt reply. Just to clarify, are you saying I can remove the supply from the 17", connect the wiring to the 20" in place of the "faulty" units wiring and start up that way (obviously with the unit safely supported)

It is interesting if they are not interchangable as people are selling used units on ebay saying they are suitable for 17" and 20"

btw, the existing power supply is not totally dead, but the imac takes several starts when cold before it will run without cutting out. When it is warmed up, it runs fine and it is ok to do a re-start if needed. (It's a bit like a car on a very cold morning). I have checked as many things as I can and reckon the power supply is getting "lazy" lol

Thanks again.
 
While you got the back cover off check for blown caps. If the caps are bulging/blown don't waste money on a new PSU unless you know how to solder caps. It even could be if its got blown caps that could be causing the power issue. But like DeltaMac said both power supplies have the same 12 pin connector and run around the same voltage so you can use the known good one for testing, but the mounts are different so it won't sit the way its supposed to. To start the machine with the back cover off for testing run a screw driver across the two gold pins left of the PSU or else that model might have had the button right next to the SMU reset button on the logic board.
 
djackmac said:
While you got the back cover off check for blown caps. If the caps are bulging/blown don't waste money on a new PSU unless you know how to solder caps. It even could be if its got blown caps that could be causing the power issue. But like DeltaMac said both power supplies have the same 12 pin connector and run around the same voltage so you can use the known good one for testing, but the mounts are different so it won't sit the way its supposed to. To start the machine with the back cover off for testing run a screw driver across the two gold pins left of the PSU or else that model might have had the button right next to the SMU reset button on the logic board.
Click to expand...

Thanks again guys. Already had the back off and all the caps seem ok, no obvious bulging etc. My machine has the start next to the SMU reset. Will leave both machines overnight and do a swap-over in the morning when cold.
 
Hi, I am new here, and I registered just to ask about this same issue. I have several G5 iMacs that a local computer store has asked me to repair. I don't have all the parts for them, so I have to rotate parts around as I fix the logic boards. I know that it is bulging capacitors in all but maybe one case. I am working on replacing the caps on 3 of the 20 inch models, and I only have 1 PSU for a 20 inch. I have swapped it around to all of them while troubleshooting, and I suspect that the psu from the 20 inch isn't working. I have a spare 17 PSU and I have done what was suggested here, where I hook it up while open just to see if the board is working. I am getting spotty results. I just want to make ABSOLUTELY sure that it isn't harmful to use a 17 inch PSU in a 20 inch model. I am freaked out that I may have repaired the bulging caps and then blown the logic boards by using the wrong PSU. Any links or info that will belay my fears are appreciated. I am really hoping that I haven't blown these boards by doing this. Help me sleep better at night by convincing me that the power units are (theoretically) interchangeable. Thanks in advance for any help.
 
BJ DuVall said:
I am freaked out that I may have repaired the bulging caps and then blown the logic boards by using the wrong PSU. Any links or info that will belay my fears are appreciated. I am really hoping that I haven't blown these boards by doing this.
Click to expand...

Apple isn't going to provide any links to let you know. I personally have all the test power supplies for every different model, but in a pinch I've swapped for ones that didn't belong and they worked fine. If the symptoms of the machine are different than before you recapped it, I'd suspect you smoked the board by sloppy desoldering/soldering.
 
thanks for the quick reply. Here is an update on what I was doing. I decided to swap a few of the parts around again, and I found that the spotty behavior was due to the HD that I was using exclusively. I was "sure" that it was a good drive and I had just recently formatted it and loaded the OS. I used known good HD and PSU from my own machine and lo and behold the two that I have replaced the caps for so far are working great with the HD and PSU from my home machine. I am extremely happy right now. I am typing this on one of the repairs that I just did. Anyway, this is a great forum and I will look here again next time I need help.
 
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